In relation to the field of the invention of the first preferred mentioned implementation, it is known that oesophageal adenocarcinoma (OAC) is rapidly increasing in frequency in the United States and other western countries. Gastroesophageal reflux disease, a benign complication caused by the stomach acid coming into the oesophagus, as a chronic condition, leads to Barrett's oesophagus (BE). It refers to the metaplasia in the cells of the lower oesophagus and in most cases is a precursor to OAC. The evolution of BE to an adenocarcinoma is observed to progress from low-grade to a high-grade dysplasia.
Medical guidelines prescribe different levels of surveillance intervals depending on the degree of dysplasia with a minimum of two biopsies per year. A typical surveillance procedure involves taking four quadrant biopsies every 2 cm towards the distal end of the oesophagus and in suspicious regions. The biopsied tissue is sent to the pathology for evaluation. With the introduction of devices such as the probe-based confocal laser endomicroscopy real-time visualization and diagnosis of suspected regions can be performed intera-operatively. High resolution narrow band imaging has also been used for diagnosis and surveillance by visual inspection of the mucosa and the subepithelium.
In each of these cases, during a follow-up inspection, the gastro-intestinal (GI) specialist is required to locate the previously biopsied or surveyed location. This problem in the literature has been termed as the re-localisation issue. Typically, the GI specialist uses the printed markings on the endoscope (commonly one mark every 5 or 10 cm along the flexible body), which can be highly unreliable and which limit his or her ability to accurately re-position the endoscope and the optical biopsy probe and hence to effectively track the disease. Due to the lack of deterministic tools for providing such re-localisation inter-operatively, the GI specialist has to survey or biopsy the entire affected oesophagus region, which prevents targeted treatments.
To the inventors' knowledge, there is no previous work or proposal which tackles this issue of re-localisation of the flexible endoscope inter-operatively. However, several approaches to track biopsy points intra-operatively exist: Baptiste Allain et al. Biopsy site re-localisation based on the computation of epipolar lines from two previous endoscopic images. In International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI), volume 12, pages 491-8. Springer, Heidelberg, January 2009; Peter Mountney et al. Optical biopsy mapping for minimally invasive cancer screening. In International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI), volume 12, pages 483-90. Springer, Heidelberg, January 2009; Baptiste Allain et al. A system for biopsy site re-targeting with uncertainty in gastroenterology and oropharyngeal examinations. In International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI), volume 13, pages 514-21, January 2010.
Each of them relies on the recovery of the 3D structure of the anatomy, to map and track the biopsy sites as they move in and out of the field-of-view of the endoscope frame. These known solutions either employ epipolar geometry or propose a simultaneous localisation and mapping (SLAM) based method. Selen Atasoy et al. (“Probabilistic region matching in narrow-band endoscopy for targeted optical biopsy”. In International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI), volume 12, pages 499-506. Springer, Heidelberg, January 2009) propose a probabilistic region matching approach in narrow-band images by using feature matches obtained from affine invariant anisotropic feature detector.
More recently Selen Atasoy et al. (“Endoscopic video manifolds for targeted optical biopsy”. IEEE transactions on medical imaging, 31(3):637-53, March 2012) propose to formulate the re-localisation as image-manifold learning process. By projecting endoscopic images on low dimensional space they propose to classify and cluster the images collected during multiple interventions into manageable segments, which they claim would aid in re-localisation of the biopsy sites. However, they do not provide any spatial relations of the extracted segments inter-operatively, and so have not sufficiently clarified the application of their result in a clinical context for re-localisation.
The inventors are of the opinion that, relying only on image based information for information extraction, that has to be mapped across multiple interventions can be highly unreliable; especially, due to temporal changes in tissue texture over multiple procedures, coupled with a highly deformable endoscopic scene, where repeatability of feature extraction, matching and tracking poses a significant challenge.
Additional methods and systems allowing to position an instrument or an endoscope within a human body are also known from the prior art, such as from U.S. Pat. No. 7,945,310, US 2005/0085718 and US 2007/0055128.
Nevertheless, these other known solutions rely on preoperative virtual 2D or 3D images, provided by an external imaging system.
These solutions thus require an important preliminary data treatment and cannot take changes in tissue texture or deformation of the targeted scene or of the environment of said scene into account.